1. Field of the Invention
The present invention relates to a failsafe sensing edge for use with automatic doors and gates.
2. The Prior Art
The use of safety devices on automatically operating doors and gates is well-known. In a usual such arrangement, for example, the door will automatically retract when an object interferes with is closing. The accepted meaning of "failsafe" in the industry is self-monitoring.
Typical designs for accomplishing this result include the use of lights with photoelectric detectors and switches which close on contact with the interfering object.
The drawbacks of arrangements currently in use include problems caused by the presence of dust, dirt and ambient lighting in photoelectric systems, and problems with humidity and moisture in the case of switches mounted in sealed electrical door edges.
A variety of United States patents have issued which disclose such safety devices.
U.S. Pat. No. 2,791,654 discloses a combined safe edge and sight guard for elevator doors using a microswitch which is closed when a cushioned edge is depressed by an interfering object.
U.S. Pat. No. 3,001,038 shows an overhead closure safety halting system utilizing an actuating bar mounted on the leading edge of the garage door to close a switch when interference occurs.
U.S. Pat. No. 3,003,303 illustrates a pneumatic safety edge for power operated doors designed to avoid the use of electrical switches. In this design, pneumatic tubes in the leading edge of the door are compressed upon making contact with an object, with a consequent increase in pressure which is transferred to a sensor located away from the door to energize the safety system.
U.S. Pat. No. 3,462,885 discloses a safety edge for a door which employs a pair of electrical conductors mounted in a compressible door edge to make contact upon the edge being compressed by an object.
U.S. Pat. No. 4,115,952 shows a safety door edge which employs a flexible channel along the door edge containing a pair of contacts which come together when the channel is compressed.
U.S. Pat. No. 4,452,009 uses a light barrier and light receivers and sender. In this arrangement, the light exit locations are cleaned each time the door is used.
U.S. Pat. No. 4,773,183 shows a contact sensitive apparatus for a power window or sun roof in which a sealed tube is employed containing a fluid which communicates with a controller to sense an interfering object.
U.S. Pat. No. 4,944,116 describes a sensor strip which acts as a light guide emitter and sensor. When the strip is distorted, it interferes with light transmission.
U.S. Pat. No. 4,953,608 discloses a safety device for roll-up doors relying on photoelectric cells.
None of the aforementioned patents teaches or suggests the present invention.
In my earlier patent, U.S. Pat. No. 5,079,417, an improved sensing edge for automatic doors and gates is disclosed, which is resistant to adverse environmental conditions such as dirt, dust, moisture, etc., and is failsafe, that is, if the edge if damaged, it can be configured to prohibit motorized operation.
The device consists of an extruded, plastic channel mounted on the leading edge of an automatic door or gate. A light source is mounted within one end of the channel and a photoswitch is mounted in the opposite end of the channel. An actuator is supported in the channel in a manner which will permit it to block the light beam when the sensing edge makes contact with an object.
While the device of my earlier invention works well, improvements have been made thereto to enhance its failsafe operation.
It is, thus, a principal object of this invention to provide an improved, failsafe or self-monitoring, sensing edge for automatic doors and gates.
It is a more particular object of the present invention to provide a more highly effective actuator for such a sensing edge.